Double cathode electron discharge device and circuits



March 29, 1938. c. H. BROWN ET AL 2,112,267

DOUBLE CATHODE ELECTRON DISCHARGE DEVICE AND CIRCUITS Filed Aug. 25, 1936 OUTPUT 0/ BEN HARMfl/V/l 1 3 FREQUENCY l l OUTPUT 0F FUNDAMENTAZ OUTPUT 0k 000 mkMa/v/cmm.

OUTPUT INVENTORS CHARLES H. BROWN AND BY WAL ER NB.ROBERTS ATTORNEY Patented Mar. 29, 1938 UNITED STATES PATENT OFFICE DOUBLE CATHODE ELECTRON DISCHARGE DEVICE AND CIRCUITS of Delaware Application August 25, 19-36, Serial No. 97,721

6 Claims.

The present invention is a continuation in part of our copending application, Serial No. 46,980, filed October 28, 1935, and relates to electron discharge device circuits which employ cold cathode negative conductance devices functioning by means of secondary emission of electrons.

In high frequency systems it is known to use an electron discharge device containing two cold cathodes coated to emit copious secondary elec- 10 trons when bombarded by other electrons, and which are oppositely disposed with respect to a central positive charged anode in the form of a metalring. In using such a, device, a guiding magnetic field in the formof a coil is employed for preventing the electrons from: immediately striking the anode.

The present invention provides, among other things, an improved cold cathode oscillation generator which dispenses withfthe use of the guiding magnetic field.

In the accompanying drawing, Figs. 1, 2, and 3 show diagrammatically different embodiments of the invention,

Referring to Fig. 1, there is shown an oscillation generator comprising an envelope E having within it two cold cathodes C and C whose con.- fronting faces are treated, or specially designed to emit copious secondary electrons upon electron bombardment. The cathodes are connected to the terminals of a resonant circuit R having an inductance L to whose midpoint is connected a battery B which maintains a central screen or perforated grid electrode P at a positive potential with respect to the cathodes. Guard rings GR. and GR surround the cathodes C, C

and are maintained at a suitable negative potential with respect to the cathodes by variable battery VB, so that the lines of electrostatic force from the cathodes C, C to the collector anode P are substantially parallel. Screen anode P presents an area of solid matter which is so small relative to the area of the perforations that the collector P will receive (prior to the time when any considerable space charge is built up within the tube) a lesser proportion of electrons passing therethrough than the ratio of gain of electrons at each impact to the number before impact. That is, if we consider a certain number of electrons about to strike the right hand cathode C, the collector P must not receive as much as the total increase in number when the secondary electrons come back through it, otherwise the number of electrons oscillating within the tube would not build up. Best results will 5 be obtained by using extremely fine wires for the collector electrode P and making the mesh as coarse as possible without upsetting the uniformity of the electrical field in the space between collector P and cathodes C, C.

It will be appreciated, of course, that since 5 the grid circuit carries current of even harmonic frequencies, a tunable circuit R may be inserted in series with the battery B and output energy at the desired even harmonic frequency may be obtained by coupling to it. If 10 desired, there may be obtained output energy 01 the fundamental frequency or of any odd harmonic thereof, merely by coupling an output circuit to the resonant circuit R, as shown in the drawing. 15

Fig. 2. discloses a modification also dispensing with the need for a magnetic field and wherein the cold cathodes C, C extend as a surface which is somewhat spherical around a small fine grid structure G which may even be a single wire. The dotted lines indicate the paths of the electrons which are not now parallel as in the structure of Fig. 1. The main thought behind Fig. 2 is that the lengths of the paths of electrons from one cathode to the other are approximately the same, 25 although there is a wide variety of paths. Output energy may be derived from the system of Fig. 2 in the same manner as derived from the system of Fig. 1.

It should be understood that the systems of 30 Figs. 1 and 2 can be stabilized as to frequency of oscillation by replacing the resonant circuit R by a mechanical resonator, either in the form of a line one-half wavelength long, a piezo-electric crystal, or a magneto-striction rod in the 35 manner taught in our copending application, supra.

Furthermore, the arrangements of the present invention may be used not only as generators of oscillations for transmitting or receiving pur- 40 poses, but also as amplifiers, detectors, or electron multipliers. The device of Fig. 1 is particularly adapted for use as a detector or an amplifier, inasmuch as the effective screen plate potential may be varied by varying the potential 45 of the negatively biased guard ring structure GR, GR which does not draw current and hence does not absorb power.

The systems of Figs. 1 and 2 can also be used as electron multipliers with slight modifications, 5 merely by enabling a beam of electrons from an external source to enter the space between the two cathodes C, C through an aperture in one of the cathodes. In such case, the resonant circuit between the cathodes C, C may be replaced by an inductance to which will be coupled an oscillator functioning at a frequency in the range, let us say, between to 100 megacycles. The midpoint of the inductance will be connected to the grid in the same manner shown in Figs. 1 and 2 to provide a positive potential thereto, and output energy will be obtained from the grid circuit by providing an impedance M in the path between the grid and the midpoint on the inductance and tapping the output leads across this impedance. Fig. 3 shows, schematically, one such arrangement wherein an oscillator O is coupled to an inductance L which connects the two cold cathodes C, C together. Output energy is obtained across resistance M in the grid circuit.

What is claimed is:

1. In combination, an electron discharge device oscillator comprising an evacuated envelope containing an anode and a pair of surfaces capable of emitting electrons on impact oppositely disposed with respect to said anode, a resonant circuit between said surfaces, a guard ring surrounding the periphery of each surface for producing lines of electrostatic force which are substantially parallel from the surfaces to the anode, means for maintaining said anode at a positive potential and said guard rings at a less potential with respect to said surfaces, and a connection f r om said means to said resonant circuit.

2. A system in accordance with claim 1, characterized in this that said anode is in the form of a grid.

3. In combination, an electron discharge device comprising an evacuated envelope containing a grid, and a pair of parallel, planar surfaces capable of emitting electrons on impact oppositely disposed with respect tosaid grid, an inductance having its terminals connected to said surfaces, a source of unidirectional current energy having its positive terminal connected to said grid and its negative terminal connected to the midpoint of said inductance, a guard ring substantially surrounding the periphery of each surface, means for maintaining said guard rings at a negative potential relative to said surfaces, an impedance connected in series between said grid and said inductance, and an output circuit coupled to said impedance.

4. An oscillation generator system in accordance with claim 3, characterized in this that a resonant circuit tuned to the desired frequency of operation of said electron discharge device is disposed between said surfaces and said inductance forms part of said resonant circuit, and another resonant circuit tuned to an even harmonic of the fundamental is disposed between said grid and inductance and said impedance forms part of said last resonant circuit.

5. A frequency multiplier system in accordance with claim 3, characterized in this that a high frequency oscillator is coupled to said inductance, and said impedance comprises a resistance.

6. In combination, an electron discharge device comprising an evacuated envelope containing a pair of substantially parallel surfaces capable of emitting electrons on impact, an electron collecting element located between said surfaces, an inductance having its terminals connected to said surfaces, a source of unidirectional energy having its positive terminal connected to said electron collecting element and its negative terminal connected to the midpoint of said inductance, a guard ringsubstantially surrounding the periphery of each surface, and means for maintaining said guard rings at a negative potential relative to said surfaces.

CHARLES H. BROWN. WALTER VAN B. ROBERTS. 

